ENIKIA INCORPORATED

Enikia Incorporated is a privately held company headquartered in Piscataway, New Jersey. A start-up founded in 1997, Enikia quickly established itself as a technological innovator and industry leader by being the first company to publicly demonstrate that high-speed in-home powerline communications was possible. After announcing that its upcoming product line would enable speeds of up to 10 Mbps, Enikia followed up by successfully unveiling its prototype units.

Enikia's product line consists of powerline Ethernet transceiver chipsets that enable data transmission speeds of 10 Mbps and above. Device OEMs purchase Enikia's chipsets or license Enikia's intellectual property in order to embed this technology into intelligent devices. Enikia's solution makes it possible for computers, as well as other "smart" appliances, to communicate with one another over the home's electrical network.

Enikia's Research and Development Efforts

Enikia's technology team invested two years of R&D to realize their vision of an elegant home networking solution that was reliable, inexpensive, and easy for the end user to operate. During the R&D period, Enikia's team conducted in-field studies of the powerline environment, gathering research data from real-world homes throughout the United States and in international locations. These studies provided some of the following discoveries that led to Enikia's novel approach for developing a high-speed powerline solution:

• The powerline is capable of reliably transmitting a signal over a wide range of frequencies.

• Noise impairments on the line can be defeated by adapting data transmission techniques to the changing environment over time.

• A combination of wiring methods can be used to transmit high-speed data signals.

By rigorously studying the effects of noise generators and appliance loading in actual homes, the Enikia team was able to statistically model these real-world environments. This knowledge was then integrated into a protocol, called ACT, which represents the core of Enikia's solution for powerline communications.

The Noise Generator and Appliance Loading Studies

The noise generator studies characterized the properties of injected noise emitted by different generators (such as a hair dryer versus a light dimmer). These studies showed that the continuous noise injected by many appliances creates a strobing effect that equates to periodic noise spikes in the time domain. (See Figure 6.5.)

Enikia was able to statistically model the pulse widths and separation of the spikes and found that the time period between spikes offers an opportunity to transmit data across the line. To exploit this opportunity, Enikia's protocol design takes a traditional Ethernet frame, segments it into small packets, and sends them in the clear time spaces between the impulse noise spikes. On the receiving side, Enikia's protocol then reassembles the segments into the original Ethernet frame, making the segmentation and reassembly process transparent to devices connected to the network.

Enikia also discovered that a combination of different wiring methods could be used. Most powerline technologies use the hot-neutral wires only. But Enikia's studies showed that the hot-ground wires could also be used for transmitting signals, and this in fact often presented a very clean channel for communication.

In the past, higher frequencies were not considered viable for powerline communications, due to the high attenuation levels. But, Enikia's field studies showed that frequencies in excess of 100 MHz can be reliably used for homes up to 5000 sq. ft. In addition, Enikia's technology includes a repeater function that extends the reach of the network.

In the United States, the FCC imposes limits on the amount of energy that can be injected on the powerline at different frequencies. The main purpose of this is to protect the rights of licensed spectrum users from interference from unintentional radiation. Enikia's signal was tested within the FCC-imposed energy limits and showed that a signal could exist on the powerline in a wide variety of frequencies without interfering with licensed users.

Development of Enikia Core Technology

The beginning of this chapter identified the powerline environment as an extremely difficult communications environment. Background noise from outside interferers, injected noise from in-home appliances, multireflective effects, and widespread signal attenuation are the primary impairments to communications. Enikia engineered a powerline technology, embodied in the following components, that addresses each obstacle and enables high-speed communications even in the harshest environments.

• The protocol processor— The protocol processor runs Enikia's ACT protocol and SST token-passing scheme.

• The DSP modem— Enikia's DSP modem is comprised of 16 digital channels and employs DBPSK and DQPSK selectively according to channel conditions.

• The analog RF front end— Enikia employs a low-cost simple analog design to couple the protocol processor and DSP modem to the powerline.

Figure 6.6 illustrates, and the following sections detail, these major elements of Enikia's technology.

ACT Protocol Overview

ACT stands for Adaptive to Channel and Time. The protocol consists of a frequency dimension, which evaluates the environment and determines the frequencies that provide the clearest path for the signal. It also includes a time dimension, which allows the signal to adapt to the ever-changing conditions on the powerline.

When viewing impulse noise on an oscilloscope, it appears as lightning strikes, where there is a clear space between every impulse. Since the noise is narrow, the network is clear for a time period between the noise spikes. In the same way that WWI planes used to shoot their machine guns time-synchronized with the rotation of their propeller blades, Enikia is able to send short packets through the clear spaces in between the impulse noise strikes. These short bursts of data are delivered very quickly.

The ACT protocol uses an environmental detector called the Received Signal Strength Indicator circuit (RSSI). This circuit aids the transmitter in identifying the beginning of a "clear" time interval as the preferred instance to launch the data across the wire. Thus, the data has a better chance of avoiding noise and maintaining a reliable link.

The ACT protocol also uses techniques to sense the density of noise on the line and adjusts the packet size and error-correction schemes accordingly. Enikia calls these different packet sizes gears since they are representative of shifting gears in a car depending on the conditions of the road. By varying the packet size in each gear, the communication throughput is optimized.

Under extreme noise conditions, the ACT protocol employs lower gears containing extensive error correction and small packets to fit in between the noise spikes. As the noise environment becomes less volatile, the ACT protocol shifts to higher, more efficient gears with larger packets sizes and less error correction.

The technology also uses up to 16 channels in parallel over a 20 MHz range. The channels adapt to the changing environment, and only the channels that communicate clearly are used at any given instant. For example, all 16 channels may be communicating at once, delivering a full 20 Mbps between transceivers. But when noise is present, a spike may flow through the 20 MHz range and eliminate the use of a few channels. The ACT protocol adapts the flow of data by eliminating certain channels, changing to a shorter packet length, changing its modulation technique, and slowing the speed of transmission so that a reliable link is maintained.

Enikia employs an additional technique, known as HOP (Historically Oriented Preference), which allows two transceivers with a poor communication link to reroute their signal through a third transceiver. HOP relates to how XCVR A and XCVR B might use another XCVR as a kind of repeater if taking that path offers better communications. HOP uses historical data to make decisions about which path through the network is best. Since powerline networks can vary greatly moment-by-moment or in a certain daily or weekly cycle, keeping this information is valuable.

By frequently evaluating the environment on the powerline, and establishing a mode of communication based on the state of the communications medium, Enikia's ACT protocol succeeds in making the network reliable.

Secure Sparse Token (SST)

The protocol processor also runs a Medium Access Protocol called Enikia's Secure Sparse Token (SST) token-passing scheme for Quality of Service considerations. The SST scheme was specifically designed for the powerline environment due to its quick token regeneration, special priority of token passing, and robustness for real-time data priorities.

Enikia's SST algorithm is based on the IEEE 802.4 token bus protocol, which has been modified by Enikia for the powerline environment.

In general, token bus offers some unique properties that are a good match for the home networking environment:

• Short token-passing times for home networks (characterized by a small diameter)

• Different levels of priorities for data

• Deterministic delay properties

• Contention-free environment

• Reduction in peak signal levels due to lack of contention

In addition, the SST provides several features that are especially desirable and often critical for the home network powerline environment. For example, the SST supports local, small-size (7-bit) addresses, as economical fronts for full-size (48-bit) Ethernet addresses. However, all nodes are aware of both (local and Ethernet) addresses of the other nodes in the network. For networks that use Ethernet hubbing, SST supports full addressing of the nodes that may reside in a network section behind a hub.

Further, to increase the efficiency of communicating nodes on the network, SST allow inactive nodes to drop out of the token passing scheme. This allows only the currently active and communicating nodes to "join" in a conversation, decreasing latency and increasing available bandwidth.

In addition, SST allows the active ring to become totally silent, eliminating token passing entirely, when no node is active. Security is addressed by using very secure three-way handshaking for token passing, and efficiency is addressed by using small control frames (approximately 30 milliseconds).

Digital DSP Modem

Enikia's DSP was designed to accomplish the following objectives:

• Be able to fit symbols in between noise spikes by utilizing fast symbol rates

• Defeat "nulls" by using narrow channel widths

• Utilize a minimum number of channels to achieve low production cost

Taking these criteria into account, Enikia engineered its DSP with channels using swift symbol rates to take advantage of the impulse noise time domain spaces, narrow channels to accept and conquer extremely deep nulls, and a limited number of channels to keep the DSP inexpensive for consumer applications.

Further, the design overcomes narrowband interferers. Most narrowband interference will only affect a single channel, rather than affecting multiple carriers or the entire signal.

The DSP Modem also implements two modulation schemes: DBPSK and DQPSK. These are used selectively according to the varying powerline environments. Under the harshest SNR (signal-to-noise ratio), the modem uses DBPSK because of its high resiliency to noise. But when signal-to-noise ratios improve, the modulation scheme switches to DQPSK for increased efficiency, doubling the potential throughput. Therefore Enikia's technology is able to balance the tradeoffs between throughput and reliability as channel conditions fluctuate. Future versions of Enikia's technology are able to employ even more efficient versions of quadrature amplitude modulation (QAM), allowing more bits per Hz and greater throughput.

Analog RF Front End

Enikia uses a low-cost, simple analog design for its RF front end. Since the DSP is responsible for the channel signal processing, Enikia only had to include a single A/D, D/A in its design. The efficiencies of the ACT protocol allow Enikia to inject low power onto the line, and therefore, the RF front end is able to use these three bands: low band (2 to 30 MHz), mid band (108 to 174 MHz), and high band (216 to 470 MHz). Even though the mid and high bands are more efficient radiators, the low injected power keeps Enikia's signal well within FCC guidelines for such frequencies.

Because of the spectrum available in these three bands, future Enikia products will offer very high throughput communications, allowing multichannel video distribution, and other very high bandwidth applications. Further, since the RF front end's design is so simple and uses relatively few components, it allows easy design of an analog semiconductor.